1. Field of the Invention
The present invention relates to a prismatic sealed rechargeable battery, and a battery module and a battery pack which include the rechargeable battery. More particularly, the invention relates to a prismatic sealed rechargeable battery in which an electrode plate assembly is accommodated in a substantially prismatic metal battery case, a battery module including a plurality of the prismatic sealed rechargeable batteries connected in series, and a battery pack including a plurality of the battery modules that are connected.
2. Description of the Related Art
In recent years, there have been demands for a rechargeable battery used as a power source of an electric vehicle including a fuel-cell vehicle and a hybrid vehicle to reduce its size and weight and to increase its capacity and power. As a sealed rechargeable battery that meets the above demands, a lithium ion rechargeable battery, a nickel-metal hydride battery and the like have been put into practical use.
In this type of sealed rechargeable battery, an electrode plate assembly including a strip-like positive electrode plate and a strip-like negative electrode plate that are wound spirally with a separator interposed between the positive and negative electrode plates is accommodated in a cylindrical metal case together with an electrolyte solution. From appropriate positions of the positive electrode plate and the negative electrode plate, a positive tab and a negative tab extend in opposite directions. The negative tab is welded to the bottom of the case, while the positive tab is welded to a sealing plate for sealing a case opening provided at the top of the case. The sealing plate is fixed to the case opening so as to tightly seal the case opening via a gasket.
Moreover, in a medium-scale rechargeable battery system formed by a plurality of sealed rechargeable batteries that are nickel-metal hydride batteries, that has a rated capacity in a range of several tens to several hundreds of ampere hours, it is known that a fin for enhancing heat dissipation of the sealed rechargeable battery is provided on a side face of a prismatic battery case, as disclosed in Japanese Patent No. 2931361.
In addition, Japanese Patent Laid-Open Publication No. 2001-93503 discloses a battery module in which a prismatic battery case of synthetic resin is provided by connecting a plurality of prismatic cases integrally at their shorter side faces. In each of the prismatic cases, an electrode plate assembly and an electrolyte solution are accommodated, thereby forming a cell. A plurality of cells are connected in series in the prismatic battered case.
However, the conventional battery using the cylindrical case has the following problems. First, the number of batteries that can be arranged within a predetermined space is small. Especially, in a case where a cooling path for preventing increase in the battery temperature is provided between the batteries, the space efficiency becomes further lower. Second, cooling capability for the center region of the battery is not good because the battery has a circular cross section. Consequently, high capacity efficiency per battery power cannot be achieved.
The prismatic sealed rechargeable battery disclosed in Japanese Patent No. 2931361 can solve the above-mentioned problems of the cylindrical battery and can enhance the heat dissipation effect by providing the fin therein. However, this prismatic sealed rechargeable battery is disadvantageous in cooling efficiency. In this prismatic sealed rechargeable battery, the fin is formed by a number of fins integrally formed on one face of a plate that is bonded at the other face to the side face of the battery case, thereby increasing the heat transfer surface area that faces a path of cooling fluid. However, since the outer face of the battery case is entirely covered by the plate, heat generated in the battery case is transferred through the wall of the battery case and the plate, so as to be dissipated from the surface of the plate or the fin. Thus, the heat transfer path becomes longer and it is difficult to sufficiently improve the cooling efficiency.
Furthermore, the prismatic sealed rechargeable battery disclosed in Japanese Patent Laid-Open Publication No. 2001-93503 has a problem that it is difficult to sufficiently increase the power of the battery. This is because the prismatic battery case is formed of synthetic resin, of which thermal conductivity is not large. Thus, it is difficult to sufficiently improve the cooling efficiency of the battery. In addition, both side faces of the prismatic battery case are easy to be expanded by the inner pressure generated in each cell. Thus, in a case of forming a battery pack by arranging a plurality of battery modules in parallel, it is necessary to arrange end plates at both ends of the array of the battery modules and to restrain the end plates with a rod or band. This increases the installation space of the battery pack and also increases the cost.